Diesel engine exhaust pollutants can be reduced by injecting a treatment fluid into the engine's exhaust stream. Such systems typically use a reductant dosing unit or “RDU” as part of a selective catalytic reduction or “SCR” system. In order for a selective catalytic reduction system to work effectively, however, the dosing device or dosing unit that injects a diesel exhaust fluid (DEF) is preferably operated when the exhaust gas and exhaust system is at elevated temperatures that support hydrolysis and thermolysis. The farther from an engine that an RDU is, the longer it takes for the exhaust gas and exhaust system to elevate to operating temperature, which lengthens the time it takes for a selective catalytic reduction system to work properly. Stated another way, the closer that a reductant dosing unit is to an engine, the more effective it will be.
Locating an RDU close to the engine subjects the device to very high temperatures. Prior art SCR systems therefore surround a diesel exhaust fluid injector with a cooled liquid, typically engine coolant, in order to limit the RDU's internal temperature.
While liquid-cooled diesel exhaust fluid injectors are known, they do not provide heat dissipation to the inlet portion of an RDU, i.e., the portion immediately adjacent to, and frequently inserted into, the exhaust stream of an engine. Extending the coolant jacket completely around the reductant dosing unit would be an improvement over the prior art.